Re: O_DIRECT support for Windows

Поиск
Список
Период
Сортировка
От Magnus Hagander
Тема Re: O_DIRECT support for Windows
Дата
Msg-id 20070117081442.D2015DCC02C@svr2.hagander.net
обсуждение исходный текст
Ответ на Re: O_DIRECT support for Windows  ("Chuck McDevitt" <cmcdevitt@greenplum.com>)
Список pgsql-patches
> People seem to be confusing sector size and cluster size.
>
> Microsoft Windows assumes sectors are 8k or less on hard drives (99% are
> 512 bytes).

Do you have any doc ref for this? I beleive you but I've been searching for docs on that and found nothing.

>
> Cluster size is the allocation unit.  On windows, this can be 512 to
> 256k (max 64k with 512 byte sectors).
> NTFS (which I think we need) is limited to 64k, last I looked.

Correct.


> On RAID devices, the allocation unit might actually be larger, but
> usually the *sector* size of these devices is still 8k or less (usually,
> they mimic the 512 byte sector size, because too much software assumes
> this)

Usually being the thing that might require an extra check.

> And that restriction is only for certain drivers and devices.  Many
> don't enforce the restriction.
> But to be safe, sector alignment is best, because there are some drivers
> that care.

exactly. so we need that check to be sure, don't we?

/Magnus


В списке pgsql-patches по дате отправления:

Предыдущее
От: "Chuck McDevitt"
Дата:
Сообщение: Re: O_DIRECT support for Windows
Следующее
От: "Magnus Hagander"
Дата:
Сообщение: Re: O_DIRECT support for Windows